1. Field of the Invention
The present invention relates generally to a tape feeder for use in chip mounters, and more particularly, to a tape feeder for use in chip mounters that includes a carrier tape feeding unit for stably feeding chips, and a chip mounting method therefor.
2. Description of the Related Art
Chip mounters are automated apparatuses used to mount a component, such as, a semiconductor chip, on a predetermined location on a printed circuit board (PCB).
Products such as integrated circuit (IC) chips 5 are susceptible to contamination by foreign matters, such as dust, for example. Hence, to be protected from foreign matters and easily handled, as illustrated in FIG. 1, the IC chips 5 are separately accommodated in an array of accommodating spaces 3b on a carrier 3 of a tape 2. The tape 2 comprising carrier 3 and IC chips 5 is wound around a reel 10 to facilitate handling and transport. The accommodating spaces 3b of the carrier 3 are covered with a tape cover 4. A plurality of transfer holes 3a are formed at predetermined intervals on one edge of a carrier 3 for advancing the carrier 3 when the reel 10 is used with a component mounter including a tape feeding unit.
FIG. 2 is a schematic perspective view of a conventional carrier tape feeding unit used in a tape feeder for chip mounters. Referring to FIG. 2, when a cylinder link 31 connected to a rod 30 of a pneumatic cylinder (not shown) advances to the left, a pivot lever 40 linked to the cylinder link 31 is clockwise pivoted a predetermined distance on a first shaft 63. The clockwise pivoting of the pivot lever 40 moves a pawl 50 downward. When the pawl 50 moves downward, a rotating force is not transmitted to a ratchet gear 60.
When the cylinder link 31 retreats to the right, the pivot lever 40 connected to the cylinder link 31 is counterclockwise pivoted a predetermined distance on the first shaft 63. The counterclockwise pivoting of the pivot lever 40 moves the pawl 50 upward. At this time, because the pawl 50 is engaged with the ratchet gear 60, the ratchet gear 60 rotates counterclockwise.
As described above, only when the cylinder link 31 retreats to the right, the ratchet gear 60 rotates at intervals of a predetermined pitch in one direction, and a sprocket 70 connected to the ratchet gear 60 is also rotated by the rotation of the ratchet gear 60. Since the teeth of the sprocket 70 are configured to mesh or interlock with the transfer holes 3a of the carrier 3 of a component carrier tape 2 (see FIG. 1), the carrier 3 moves at intervals of a predetermined distance and is simultaneously unwound from around the reel 10. At this time, the tape cover 4 is peeled off from the carrier 3 to expose the spaces 3b housing the chips 5 and the tape cover 4 may be wound around a winding unit (not shown). The exposed IC chips 5 are absorbed (i.e., picked up) by an absorbing (e.g., a vacuum) nozzle (not shown) of a chip mounter (not shown), transferred to a predetermined location on a PCB, and mounted on the PCB.
In a conventional carrier tape feeding method, a feeding velocity of the tape 2 is constant from the initial feeding time to the final feeding time. Constant velocity tape feeding often causes an impact (e.g., a sudden jolt) to be generated at ends of the teeth of the sprocket 70 upon the retreat of the cylinder link 31. The impact causes fine components to be turned over or causes them to assume wrong postures prior to being picked up. A shutter 80 is introduced to solve these problems.
When the cylinder link 31 retreats to the right, the shutter 80 advances in the same direction as the direction in which the IC chips 5 move, thereby preventing the IC chips 5 from flipping. On the other hand, when the cylinder link 31 advances to the left, the shutter 80 retreats in the direction opposite to the direction in which the IC chips 5 move, thereby exposing the IC chips 5 so that the absorbing nozzle can pick up the IC chips 5.
However, even when employing the shutter 80, minute components such as, for example, components of a size approximately 0.4×0.2 (mm) may be slightly lifted from the accommodating spaces 3b due to an impact. Hence, when retreating, the shutter 80 rather contacts the components and causes wrong postures or orientations of the components. When the shutter 80, sliding on a guide 90, is installed higher than a predetermined location due to a manufacturing tolerance, the shutter 80 cannot prevent overturn of the minute components.
Until now, to solve these problems the overall speed of feeding fine components has been decelerated, affecting the whole feeding and mounting process. Disadvantageously, overall deceleration of feeding components causes low work efficiency.